Increasingly, ruthenium (Ru) metal is an important material in semiconductor device fabrication, and ruthenium layers, films, and other structures may be incorporated into semiconductor components and elements such as wires, electrical contacts, electrodes, capacitors, transistors, and diodes. Ruthenium also is used in many other applications and, for example, may be employed as building material for masks, as a coating on mirrors, to provide a surface for catalysis, or may be applied to objects by chemical or physical vapor deposition techniques so as to provide a surface coating having advantageous wear or corrosion properties.
One particularly advantageous application of ruthenium metal is its use in the formation of electrode layers in the fabrication of oxide high dielectric capacitors, wherein the ruthenium metal is typically applied either as a thin film by sputter deposition or as a conformal layer by metal organic chemical vapor deposition. Ruthenium is a conductive metal that oxidizes to form a similarly conductive ruthenium dioxide (RuO2) layer on the surface of the existing ruthenium metal. Therefore, when an oxide high dielectric capacitor is formed, the surface of a ruthenium layer provided as the electrode material will not form a secondary dielectric layer when oxidized to RuO2 during the oxygen anneal of the high dielectric material. The fact that ruthenium's oxide form is conductive distinguishes it from other conductive metal film materials such as, for example, tungsten, tantalum, and titanium, all of which form relatively non-conductive oxide layers. Certain other possible capacitor electrode materials do not oxidize during the application of an oxidizing anneal to the high dielectric material. One such capacitor electrode material is platinum. However, ruthenium provides advantages over platinum when used as a capacitor electrode in that platinum has a tendency to leak charge, a property that is not exhibited to the same degree by ruthenium.
In fabricating semiconductor devices incorporating a ruthenium metal film, such as, for example, the above-described oxide high dielectric capacitors, it may be necessary to etch, pattern, dissolve, or otherwise remove at least a portion of the ruthenium metal film or its dioxide so as to provide a suitably configured electrode or other structure or to completely remove such a film as an aid in recovering improperly coated devices. When ruthenium metal is provided on an object by chemical vapor deposition, physical vapor deposition, or other deposition techniques, a film or other deposit ruthenium metal and/or ruthenium dioxide may be deposited on surfaces of the tools, components, and apparatuses used in the deposition process, and it may be desirable to remove the ruthenium metal and/or ruthenium dioxide therefrom.
However, both ruthenium metal and ruthenium dioxide are resistant to removal by known wet etching techniques, and none of the wet etchants traditionally used in semiconductor device processing, including aqua regia and piranha, will dissolve ruthenium. In fact, both the CRC Handbook and the Merck Index list ruthenium metal as being insoluble in strong acids and oxidizers and as being soluble only in molten alkali salts, harsh etchants unsuitable for many applications, including semiconductor processing. Currently, if a layer or film of ruthenium metal or ruthenium dioxide must be etched or patterned in the fabrication of a semiconductor device, one of a number of dry etch procedures is used, including oxidizing argon plasma and O2 plasma etch procedures. However, the use of any of those dry etch procedures to remove ruthenium metal or ruthenium dioxide results in the formation of the explosive compound ruthenium tetroxide (RuO4). The ruthenium tetroxide must be removed or otherwise prevented from building to dangerous levels during the dry etch procedures, and this may increase the complexity and expense of such procedures.
Although ruthenium metal and ruthenium dioxide layers, films, and other structures are useful in semiconductor device fabrication, the use of such structures in that application has been limited because of the inability to satisfactorily etch or pattern the structures using wet etch techniques and the distinct disadvantages resulting from use of dry etch techniques. For like reasons, it has heretofore been difficult to remove undesirable films, layers, deposits, or other structures of ruthenium metal and ruthenium dioxide from tools and other objects. Accordingly, a need exists for an improved method for etching, patterning, or otherwise removing at least a portion of a ruthenium metal or ruthenium dioxide structure.